Photonic crystal fibers allow for high power laser/amplifier operation due to the large core diameters which still offer single-mode output. Such high power laser/amplification operation is due to reduction in the numerical aperture (NA) of the fiber. Reduced numerical aperture (in some embodiments <0.03) of the fibers render those fibers vulnerable to bending losses, and therefore are kept straight. Such fibers, while they can be coiled, must be coiled at large radii, typically over 25 cm. Typical doped fiber lengths configured to allow for efficient pump absorption are on the order of 1 to several meters long. This length, combined with the large coil radius of such fibers renders packaging impossible.
An alternative method employs photonic crystal rods. Photonic crystal rods have a photonic fiber core and a glass jacket that prevents the photonic fiber core from bending. The photonic fiber core typically has a numeric aperture smaller than that of Photonic crystal fibers. It is to accommodate these smaller numeric apertures that the glass shell is utilized. Such rods are typically between 0.5 and 1 m in length, again making compact packaging untenable. In some versions, photonic crystal fibers may comprise a fiber through which pass a plurality of air holes around a solid or hollow core, while in other configurations, photonic crystal fibers comprise a core of a different material than that of the shell.
Lengths for such known systems are typically greater than 0.5 m in length, so compact packaging is simply not possible. Current photonic fiber systems use long fiber lengths, such fiber lengths result in non-linear processes within the optical fiber. These non-linear processes result in decreased output power.
What is needed, therefore, are techniques for providing compact packaging and high non-linear threshold for Photonic crystal fiber systems configured for high power/energy laser applications.